Why can't I fill in a password for a WatchGuard SSL VPN in Devolutions' Remote Desktop Manager?

I'm not sure if questions about Remote Desktop Manager from Devolutions can be asked here.

I'm setting my first steps in this tool, and I have managed getting to work with different RDP sessions, some based on a Microsoft based VPN. It is possible to fill in a password, as you can see:

Image may be NSFW.
Clik here to view.

Now I would like to do the same for a Watchguard SSL VPN, but there it seems not to be possible to fill in a password, as you can see:

Image may be NSFW.
Clik here to view.

Am I doing something wrong? Is it not possible to add a password for a WatchGuard SSL VPN (that would really surprise me)?

Thanks in advance